This invention relates to an optic fiber wavelength multiplexer-demultiplexer or router, liable to be used as a component in optic fiber teletransmission units.
Such multiplexers-demultiplexers are already known, as described, then gradually perfected, in particular in the French patents FR-2.543.768, FR-2.519.148, FR-2 479.981, FR-2.496.260 and in the European patent EP-0.196.963.
By optic fiber multiplexer-demultiplexer, we mean devices in which input and output luminous waves are propagated by optic fibers.
The invention also relates to the optic fiber routers in which a variable number of input flows, each with a particular wavelength, propagated by spatially distinct optic fibers, are addressed on a possibly different number of output fibers.
In these different devices, coupling is made via a dispersing system, for a given wavelength between an output fiber and an input fiber.
Thus is defined a channel which exhibits of course a certain spectral width .DELTA..lambda..
Powerful multiplexers-demultiplexers or routers must simultaneously enable operating a vast number of channels, each of these channels, centered round a wavelength .lambda., must exhibit a spectral width .DELTA..lambda. which is as large as possible, while avoiding any crosstalk.
There is a crosstalk when a portion of the energy from a channel is partially mixed with the energy from an adjacent channel. It is well known that the crosstalk disturbs the communications and that the devices exhibiting an excessive rate of crosstalk are useless in practice.
In order to simplify the description, the device according to the invention will be qualified as a multiplexer-demultiplexer, whereas it should be noted that it may relate to a multiplexer, a demultiplexer or a router.